The expression you've provided appears to be slightly ambiguous due to formatting. However, I will interpret it as follows:

\[
X^3 + 3X^2Y + 3XY^2 + Y^3 + X^3 + 3X^2Y + 3XY^2 + Y^3
\]

Let's simplify this expression step by step.

1. Combine like terms:

- The \(X^3\) terms: \(X^3 + X^3 = 2X^3\)
- The \(3X^2Y\) terms: \(3X^2Y + 3X^2Y = 6X^2Y\)
- The \(3XY^2\) terms: \(3XY^2 + 3XY^2 = 6XY^2\)
- The \(Y^3\) terms: \(Y^3 + Y^3 = 2Y^3\)

Putting it all together, we get:

\[
2X^3 + 6X^2Y + 6XY^2 + 2Y^3
\]

2. Factor out the common coefficient. The terms \(2\) can be factored out:

\[
2(X^3 + 3X^2Y + 3XY^2 + Y^3)
\]

3. The expression inside the parentheses resembles the expansion of \( (X + Y)^3 \):

\[
X^3 + 3X^2Y + 3XY^2 + Y^3 = (X + Y)^3
\]

Thus, the entire expression can be simplified to:

\[
2(X + Y)^3
\]

So, the final simplified form of your expression is:

\[
2(X + Y)^3
\]