Regex matching in shell script

Question

Here is a snippet from my shell script -

regex="<version>([0-9]*)\.([0-9]*)\.([0-9]*)([^<]*)<\/version>.*"

#some unrelated lines of code

    echo $(grep -m 1 "<version>" $1)
    if [[ $(grep -m 1 "<version>" $1) =~ $regex ]]
    then
        main_version = "${BASH_REMATCH[1]}"
        feature_version = "${BASH_REMATCH[2]}"
        patch_version = "${BASH_REMATCH[3]}"
        tag = "${BASH_REMATCH[4]}"
    else
        echo "$1: Version not Found" >&2
    fi

But it is showing me the following output -

<version>1.1.7-release</version> <!-- ABC version -->
abc/xyz/pom.xml: Version not Found

But according to my understanding, regex should match with the output of grep(i echoed it to terminal for better clarity). So can someone tell what am i doing wrong?