Delighted club chairman Gareth Saunders said: “It felt like an eternity coming; everyone expected us to win it, but we took it one game at a time and are just relived to get it out of the way.
“We finished last season in good form, winning eight games on the trot, so it was always our plan to try and win the league.”
On the standout results of the season, Saunders picked out the 42-5 win over WRU National Plate winners Penallta on September 17 and the 15-9 victory at Brynmawr on January 7.
He said: “We scored 40 points against Penallta but it could have been 60 had we taken our chances.
“We’d had some really tough ones away but I think the victory at Brynmawr stands out because we weren’t playing well that day but we just managed to scrape over the line.
“That was probably equally as important as the big win over Penallta at home.”
Rhydyfelin will now gear up for the two-legged play-off with One East Central winners Treorchy – with promotion to the WRU National Championship at stake.
“They’re going to be two tough games,” added Saunders. “Treorchy are a quality side and they’ve already proved that by beating us once this year 16-10 in the quarter-finals of the Mid District Cup.”