Josh Adams has been suspended for Wales' first two matches of the Six Nations following a breach of Covid-19 protocols.
Adams attended a gathering with his immediate family present on Sunday, the day after the full Wales squad were released from camp ahead of their Six Nations opener with Ireland.
The squad linked back up on Tuesday at their Vale Resort base and the Welsh Rugby Union say the breach was immediately raised and acted upon.
Wales head coach Wayne Pivac said: "We are extremely disappointed with the breach and have acted robustly and swiftly to take all appropriate measures.
"All players and management have received detailed briefings and education regarding our protocols, and everyone has a responsibility to abide by the rules.
"On this occasion, Josh has made an error of judgement, he made a mistake and he has shown immediate remorse.
"He was present at a small, immediate family gathering to celebrate a milestone with those close to him, but that is against the rules and action had to be taken."
Cardiff Blues wing Adams has won 29 caps and scored 14 Test tries.
The 25-year-old was the top try-scorer at the 2019 World Cup in Japan with seven tries.
Adams, who has been released from the Wales training camp, said: "I would like to apologise unreservedly.
"When out of camp, at the weekend, I made an error of judgement. I attended a small gathering of immediate family to celebrate a family milestone.
"It was wrong to do this. I'm aware that everyone needs to follow the rules and being in the public eye I have a responsibility to lead by example and I've fallen short on this occasion.
"I'd like to apologise to my team-mates and to our supporters for my mistake."
The WRU said all members of the Wales squad have received extensive Covid protocol briefings and education.
A WRU statement said: "We will continue with our programme, which has been very effective to date, and remind everyone of their responsibility to not only adhere to the extensive measures in place but also to set an example.
"We will work with Josh in relation to his integration back into camp following a further testing and re-education process."
The Wales squad's latest round of Covid-19 tests on Wednesday all returned negative results.
Wales start their Six Nations campaign against Ireland at Cardiff on Sunday before playing Scotland at Murrayfield six days later.