The midfielder cancelled out Andy Reid's opener at Vicarage Road to end the Reds' 100 per cent start to the Championship season and secure a share a spoils.
It was a moment to remember for McGugan, who came through the youth ranks at Forest and enjoyed over 200 appearances for his hometown club before making a summer switch to Watford.
"It's nice to score any time, but against your former team, and the fact it was a free-kick - which is one of the things I try and practice as much as possible - it was particularly pleasing," he told the club's official website.
"I know (Karl) Darlow (Forest goalkeeper) well and I know his favourite side, and I just told myself to get it on target and it's got a chance of going in. I picked my corner, I knew where I wanted to put it, and it went there.
"It was the first free-kick we had and I grabbed the ball straight away, but me and Almen (Abdi) have got a good relationship regarding free-kicks, whoever thinks it's the best opportunity at the time will take it. Luckily enough it was my turn and I put it away.
"It's an emotional day for me and it was the first time I've ever done it (played against Forest) so it was a bit weird, but it's over now. I'm glad I got the goal and I think the point was fully deserved."
- Sports & Recreation